Last season we noticed our transmission fluid turned milky. We went for the easy fix first and put a new heat exchanger in just in case that was leaking. Flushed the tranny 3 times. Within 5 uses the fluid was milky again. This didn't surprise us, but it was worth a shot for a couple hundred bucks.

From research on this and other sites I believe the two potential issues are

1) leaky prop shaft seal(packing?) causing water to be 'pulled' up the driveline, through the hull into the tranny

2) leaky main seal

Because there is a small amount of oil in the bilge I believe it is the later. I am pretty frustrated that a boat that is only 6 years old with under 350 hours is already having this problem. Of course it is no longer under warranty so I will be paying the bill for this defect, not MasterCraft. (please someone tell me MasterCraft has done the honorable thing and issued a recall on their defective seals, a 24-pac of your choice will be delivered to your doorstep)

I spoke to guy at the local shop, he seemed familiar with the defect and said to replace the main seal he will need to pull both the engine and the tranny and provided an estimate of about $2200. This includes flushing the tranny several times to get as much water out as possible.

I read that MasterCraft changed from a 1-piece main seal to a 2-piece main seal to make this maintenance easier so the engine and tranny need to be separated, but not completely pulled.

Can anyone confirm if this is true?
Does the $2200 estimate to fix the problem seem reasonable?
Or if my searching was bad, can you point me in the direction of information on this issue that answers the question?

Thanks!

KYBOOL

03-28-2012, 04:20 PM

That would be a transmission cooler, not a heat exchanger. My mistake.

CantRepeat

03-28-2012, 05:21 PM

Is there enough water in the bilge that it covers up the back of the transmission?

If the packing around the prop shaft is leaking water it would need to be high enough to cover the back of the trans for it to be pulled into the transmission while it was cooling down.

I would NOT toss $2200 at it until you know for sure why and how this is happening.

Jeff d

03-28-2012, 05:41 PM

That would be a transmission cooler, not a heat exchanger. My mistake.
Well, technically you were right since a transmission cooler is a heat exchanger.

FrankSchwab

03-28-2012, 07:28 PM

I agree with CantRepeat. There are, to the best of my knowledge, only four paths that water can get into the tranny:
1. Through the transmission cooler. By far the most likely.
2. Through the transmission output shaft seal. This can only happen if there's (I would guess) a foot of water in the bilge - it has to at least be as high as the seal, and most likely has to completely cover the seal.
3. Through the transmission input shaft seal. This can only happen if the water in the bilge is up to the level of the crankshaft on the engine.
4. Through the transmission vent. There's an air vent on the top of the transmission to allow pressure/vacuum buildup to equalize. This can only happen if the water in the bilge is covering the transmission. You'd probably notice this, because the floor would be covered with water also!

The transmissions in our boats aren't built to work underwater. Having water leak through any of the seals isn't surprising if water is covering the seal; it might indicate a blockage in the vent, but might not.

So, if it isn't the cooler, then you must have a LOT of water in the bilge. I would take the boat out and check how much water is in the bilge every ten minutes or so. If you haven't been paying close attention to the bilge, this could be a completely different problem - perhaps your bilge pump has failed, or the dash switch has been moved from "auto" to "off". Perhaps your propshaft packing has dried out, and water is streaming in through the stuffing box. Perhaps both your old cooler AND your new cooler are defective.

You say you've got oil in the bilge also - is it just a sheen of oil on top of the water, or is it a solid layer on the bottom of the bilge? Is it engine oil or transmission oil (note that this is a trick question - your transmission could have either ATF or 15w-40 engine oil in it...)? If the transmission output shaft seal is bad and leaking oil, water still can't get in unless you have a LOT of it in the bilge.

Let us know what you find...

/frank

CantRepeat

03-28-2012, 07:55 PM

Great post Frank.

I agree, there would have to be bunch of water in the bilge for water to get into the trans if the cooler is not leaking.

Remember, just because it's new doesn't mean it is not leaking.

76S&S

03-29-2012, 09:42 AM

In my 02' the trans sits less than an inch off of the floor. A few inches of water in the bilge will get up on the trans seal. The seal doesn't have to be submerged competely for the transfer of water/oil to take place, only the bad area of the seal has to be under water. The heat/cooling will push/pull oil/water in and out of the trans.

My trans seal went out two years ago, milk in the trans, oil in the bilge. My dealer pulled the trans only and the price tag was roughly half of what you were quoted.

mikeg205

03-29-2012, 09:58 AM

For $2200 - or even $1100 I would learn to change the seal and have a friend and I do it...then celebrate with our favorite brew...of course after returning the engine lift if needed.

KYBOOL

03-29-2012, 02:48 PM

Thank you for all the help guys, and the very detailed list of options Frank. I wish I had done a better job monitoring the water in the bilge last year. And I wish I had watched the tranny fluid the first few trips out.

I do think at least one of the bilge pumps is broken so it is very possible there is enough water sitting around to be the culprit.

When the old tranny cooler was pulled they pressure-tested it and didn't find any issues. Since it was pulled we decided to replace it anyways. I am pretty sure this isn't the cause.

There isn't large deposits of oil or red tranny fluid in the water, just a trace of rainbow on the surface.

Will be taking a deeper dive into the issue this weekend now that the boat is out of storage. Will keep you posted. Thanks again!

Jeff d

03-29-2012, 03:38 PM

There isn't large deposits of oil or red tranny fluid in the water, just a trace of rainbow on the surface.

That's usually how it is even in a really clean bilge.

FrankSchwab

03-30-2012, 09:18 PM

One thing to look for is the transmission fluid level - if water is getting in from the cooler, a lot of times the fluid level will rise as the water comes in. Not always though - my cooler was leaking fluid out, but not a drop of water got into the transmission.

I will agree with Jeff that there will ALWAYS be a sheen of oil on the surface of bilge water, even on a clean, well maintained boat.